Addressing the issue of exposure to primary pollution in urban areas: Application to Greater Paris

Abstract This work aims to highlight the importance of refining the calculation of exposure to primary pollutants in dense urban areas, by taking into account both pollutant concentration heterogeneity at the street scale, and individual mobility during the day. To address this issue, we have set up an urban modeling chain based on the OLYMPUS and CHIMERE models, and offering innovative statistical work on simulation data. OLYMPUS is an emission modeling system that produces mobility matrices for individuals in a city through an activity-based approach of the travel demand. CHIMERE is a chemistry-transport model that uses anthropogenic and biogenic emissions, meteorological fields and large-scale chemical fields to produce hourly pollutant concentration fields in a given area. A statistical post-processing of CHIMERE output data has been developed to create sub-grid variability for NO2 and PM10 concentrations - mainly related to the proximity of busy roads, and its results have been crossed with daily mobility matrices for every citizen, in order to refine our estimate of the individual exposure budget. This urban modeling platform has been implemented over Greater Paris. The results show that such approach considerably expands the range of individual exposure values and raises the question of recurrent exposure of city dwellers to very high levels of pollution, even during reduced periods of time during the day. They also introduce the issue of environmental inequalities linked to practices and constraints of dwelling place, mobility and work, which need to be apprehended by new modeling approaches.